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Abstract:

An optical writing control apparatus controls a light source to draw a
correction pattern for correcting a parameter value of an image forming
mechanism, detects the correction pattern transferred onto a conveyance
member from a photosensitive member based on an output signal of a
sensor, and corrects the parameter value based on the detected correction
pattern; stores chromatic color progress information indicating a
progress for a chromatic color mechanism corresponding to a chromatic
color image occurring from when the correction operation was carried out
and achromatic color progress information indicating a progress for an
achromatic color mechanism corresponding to an achromatic color image
occurring from when the correction operation was carried out; and stores
a necessary threshold to determine that the correction operation is
necessary and an unnecessary threshold to determine that the correction
operation is unnecessary for the chromatic color progress information and
the achromatic color progress information.

Claims:

1. An optical writing control apparatus that controls a light source
emitting a light beam onto a photosensitive member to cause the light
source to draw an electrostatic latent image on the photosensitive member
in an image forming apparatus that develops the electrostatic latent
image drawn on the photosensitive member and forms an image, the optical
writing control apparatus comprising: a parameter correction part that
controls the light source to cause the light source to emit the light
beam and draw a correction pattern used for a correction operation of
correcting a parameter value of an image forming mechanism of the image
forming apparatus, detects the correction pattern transferred onto a
surface of a conveyance member based on an output signal of a sensor that
obtains imaging information of the surface of the conveyance member onto
which an image developed on the photosensitive member is transferred, and
corrects the parameter value based on the detected correction pattern; a
progress information storage part that stores chromatic color progress
information indicating a progress having occurred from when the
correction operation for a chromatic color mechanism of the image forming
mechanism corresponding to a chromatic color image was carried out and
achromatic color progress information indicating a progress having
occurred from when the correction operation for an achromatic color
mechanism of the image forming mechanism corresponding to an achromatic
color image was carried out; and a threshold storage part that stores a
necessary threshold used to determine that the correction operation is
necessary and an unnecessary threshold used to determine that the
correction operation is unnecessary, with respect to the chromatic color
progress information and the achromatic color progress information.

2. The optical writing control apparatus as claimed in claim 1, wherein
the parameter correction part determines whether the correction operation
is necessary separately for the respective ones of the chromatic color
mechanism and the achromatic color mechanism by comparing the respective
ones of the chromatic color progress information and the achromatic color
progress information with the necessary threshold, and it is determined
that the correction operation is necessary for both of the chromatic
color mechanism and the achromatic color mechanism in a case where any
one of the chromatic color progress information and the achromatic color
progress information has become equal to or more than the necessary
threshold and the other has a value between the unnecessary threshold and
the necessary threshold.

3. The optical writing control apparatus as claimed in claim 2, wherein
the parameter correction part determines, in a case where the image
forming apparatus operates in an achromatic color preference mode in
which a chromatic color image is converted into an achromatic color image
and the achromatic color image is output, that the correction operation
is necessary only for the achromatic color mechanism even in the case
where the achromatic color progress information has become equal to or
more than the necessary threshold and the chromatic color progress
information has a value between the unnecessary threshold and the
necessary threshold.

4. The optical writing control apparatus as claimed in claim 3, wherein
the parameter correction part determines, in a case where the image
forming apparatus operates in the achromatic color preference mode and a
page of an achromatic color image is to be output subsequently, that the
correction operation is necessary only for the achromatic color mechanism
even in the case where the achromatic color progress information has
become equal to or more than the necessary threshold and the chromatic
color progress information has a value between the unnecessary threshold
and the necessary threshold.

5. The optical writing control apparatus as claimed in claim 1, wherein
the correction operation is carried out when an image is formed and
output in the image forming apparatus, and the parameter correction part
has a function of adjusting an amount of light of a sensor light source
of a sensor that obtains imaging information of the surface of the
conveyance member, the sensor light source irradiating the surface of the
conveyance member, and a function of continuously turning on the sensor
light source for a predetermined period of time after the completion of
the image being formed and output in the image forming apparatus, and
carries out adjusting of the amount of light of the sensor light source
in a case where the sensor light source having been turned off is turned
on when the correction operation is carried out.

6. The optical writing control apparatus as claimed in claim 5, wherein
when the correction operation is carried out, the parameter correction
part carries out the adjusting of the amount of light of the sensor light
source in a case where the sensor light source has been turned on and
light amount adjustment progress information that indicates a progress
having occurred after adjusting of the amount of light of the sensor
light source was carried out last has become equal to or more than a
predetermined threshold.

7. The optical writing control apparatus as claimed in claim 1, wherein
the correction operation is carried out when an image is formed and
output in the image forming apparatus, and when the correction operation
is carried out when an image is formed and output in the image forming
apparatus, the parameter correction part carries out adjusting of the
amount of light of the sensor light source in a case where a job of
forming and outputting an image for which adjusting of the amount of
light of the sensor light source was carried out last is different from a
job of forming and outputting an image for which the current correction
operation is carried out.

8. The optical writing control apparatus as claimed in claim 7, wherein
when the correction operation is carried out when an image is formed and
output in the image forming apparatus, the parameter correction part
carries out adjusting of the amount of light of the sensor light source
in a case where a job of forming and outputting an image for which
adjusting of the amount of light of the sensor light source was carried
out last and a job of forming and outputting an image for which the
current correction operation is carried out are included in a series of
jobs, and light amount adjustment progress information that indicates a
progress having occurred after adjusting of the amount of light of the
sensor light source was carried out last has become equal to or more than
a predetermined threshold.

9. The optical writing control apparatus as claimed in claim 1, wherein
the correction operation is carried out when an image is formed and
output in the image forming apparatus, and the parameter correction part
includes a function of adjusting an amount of light of a sensor light
source of the sensor that obtains imaging information of the surface of
the conveyance member, the sensor light source irradiating the surface of
the conveyance member, and a function of continuously turning on of the
sensor light source for a predetermined period of time after the
completion of the image being formed and output in the image forming
apparatus, when the correction operation is carried out, the parameter
correction part carries out adjusting of the amount of light of the
sensor light source in a case where the sensor light source has been
turned on and light amount adjustment progress information that indicates
a progress having occurred after adjusting of the amount of light of the
sensor light source was carried out last has become equal to or more than
a first predetermined threshold, when the correction operation is carried
out when an image is formed and output in the image forming apparatus,
the parameter correction part carries out adjusting of the amount of
light of the sensor light source in a case where a job of forming and
outputting an image for which adjusting of the amount of light of the
sensor light source was carried out last and a job of forming and
outputting an image for which the current correction operation is carried
out are included in a series of jobs, and the light amount adjustment
progress information that indicates the progress having occurred after
adjusting of the amount of light of the sensor light source was carried
out last has become equal to or more than a second predetermined
threshold, and the first predetermined threshold is smaller than the
second predetermined threshold.

10. The optical writing control apparatus as claimed in claim 1, wherein
the parameter correction part corrects the parameter value of timing of
causing the light source to emit light based on a period of time from
when drawing of the correction pattern is started up to when the
correction pattern is detected from the output signal of the sensor.

11. The optical writing control apparatus as claimed in claim 1, wherein
the parameter correction part corrects the parameter value of a voltage
to be applied for developing the electrostatic latent image drawn on the
photosensitive member based on density of the detected correction
pattern.

12. The optical writing control apparatus as claimed in claim 1, wherein
the parameter correction part corrects the parameter value of timing of
causing the light source to emit light based on a period of time from
when drawing of the correction pattern is started up to when the
correction pattern is detected from the output signal of the sensor, the
parameter correction part corrects the parameter value of a voltage to be
applied for developing the electrostatic latent image drawn on the
photosensitive member based on density of the detected correction
pattern, and the necessary threshold used to determine that the
correction operation to correct the parameter of the timing is necessary
is smaller than the necessary threshold used to determine that the
correction operation to correct the parameter of the voltage is
necessary.

13. The optical writing control apparatus as claimed in claim 12, wherein
the parameter correction part determines that the correction operation to
correct the parameter of the timing is necessary when having determined
that the correction operation to correct the parameter of the voltage is
necessary.

14. An image forming apparatus including the optical writing control
apparatus claimed in claim 1.

15. A control method of an optical writing control apparatus that
controls a light source emitting a light beam onto a photosensitive
member to cause the light source to draw an electrostatic latent image on
the photosensitive member in an image forming apparatus that develops the
electrostatic latent image drawn on the photosensitive member and forms
an image, the control method of the optical writing control apparatus
comprising: controlling the light source to cause the light source to
emit the light beam and draw a correction pattern used for a correction
operation of correcting a parameter value of an image forming mechanism
in the image forming apparatus, detecting the correction pattern
transferred onto a surface of a conveyance member based on an output
signal of a sensor that obtains imaging information of the surface of the
conveyance member onto which an image developed on the photosensitive
member is transferred, and correcting the parameter value based on the
detected correction pattern; storing chromatic color progress information
indicating a progress having occurred from when the correction operation
for a chromatic color mechanism of the image forming mechanism
corresponding to a chromatic color image was carried out and achromatic
color progress information indicating a progress having occurred from
when the correction operation for an achromatic color mechanism of the
image forming mechanism corresponding to an achromatic color image was
carried out; and storing a necessary threshold used to determine that the
correction operation is necessary and an unnecessary threshold used to
determine that the correction operation is unnecessary, with respect to
the chromatic color progress information and the achromatic color
progress information.

16. The control method of the optical writing apparatus as claimed in
claim 15, further comprising: determining whether the correction
operation is necessary separately for the respective ones of the
chromatic color mechanism and the achromatic color mechanism by comparing
the respective ones of the chromatic color progress information and the
achromatic color progress information with the necessary threshold, and
determining that the correction operation is necessary for both of the
chromatic color mechanism and the achromatic color mechanism in a case
where any one of the chromatic color progress information and the
achromatic color progress information has become equal to or more than
the necessary threshold and the other has a value between the unnecessary
threshold and the necessary threshold.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical writing control
apparatus and a control method of an optical writing apparatus, and, in
particular, to reduction of downtime that occurs for carrying out
adjustment of the optical writing apparatus.

[0003] 2. Description of the Related Art

[0004] Recently, computerization is promoted and an image processing
apparatus such as a printer and a facsimile machine to be used for
outputting computerized information and a scanner or such to be used for
computerizing documents may become an indispensable apparatus. Such an
image processing apparatus may be, in many cases, a MFP (MultiFunction
Peripheral) that is useable as a printer, a facsimile machine, a scanner
and a copier by having an imaging function, an image forming function, a
communication function and so forth in a single machine.

[0005] As an image forming apparatus that is one of such image processing
apparatuses and is used to output computerized documents, an image
forming apparatus in an electrophotographic type is widely used. The
image forming apparatus of the electrophotographic type is such that an
electrostatic latent image is drawn on a photosensitive member as a
result of the photosensitive member being exposed, a toner image is
formed as a result of the electrostatic latent image being developed by
using developer such as toner, the toner image is transferred to paper
and thus, the image is output as being formed on the paper.

[0006] In the image forming apparatus of the electrophotographic type,
adjustment is carried out such that the image is formed at a precise
position on the paper as a result of timing of exposing the
photosensitive member and drawing the electrostatic latent image are made
to be coincident with timing of conveying the paper. Further, in an image
forming apparatus of a tandem type in which plural photosensitive members
are used to form a color image, adjustment of exposure timing between the
photosensitive members of respective colors is carried out such that
images developed on the photosensitive members for the respective colors
are superposed on each other precisely (see Patent Document 1: Japanese
Laid-Open Patent Application No. 2008-299311). Hereinafter, these
adjustment processes will be generally referred to as position error
correction.

[0007] As another adjustment operation in the image forming apparatus in
the electrophotographic type, there is an operation (hereinafter,
referred to as gradation correction) of adjusting a gradation of an image
to be formed, i.e., densities of the image. In the gradation correction
of an image, plural adjustment patterns having different densities are
formed on the photosensitive member of each color, optical sensors are
used to read the adjustment patterns, and bias voltages (i.e.,
development bias) of the photosensitive members (drums) are adjusted so
that appropriate gradation is obtained.

[0008] In correction of drawing parameters (hereinafter, referred to as
drawing parameter correction) such as the position error correction and
the gradation correction described above, toner is consumed since the
adjustment patterns, i.e., patterns for the adjustment, are formed.
Further, the drawing parameter correction may be carried out, for
example, at a time of power being turned on in the image forming
apparatus, at a time of returning from a power saving mode, or before
carrying out forming and outputting an image. In a case where the drawing
parameter correction is carried out before forming and outputting, for
example, a monochrome image, the drawing parameter correction for the
other colors is not necessary. If drawing parameter correction for the
other colors is carried out, the toner is consumed as mentioned above,
and the toner of the colors other than black is uselessly consumed.

[0009] An image forming apparatus has been proposed (see Patent Document
2: Japanese Laid-Open Patent Application No. 2008-151855) as technology
to control such useless consumption of color toner in which switching can
be made between a monochrome control mode in which gradation correction
is carried out only for black toner and a color control mode in which
gradation correction is carried out for full color.

[0010] In a case of using the technology disclosed by Patent Document 2,
both the gradation correction only for black toner and the gradation
correction for full color may be carried out within a short span of time
when a job for forming and outputting an image of full color is input and
the gradation correction for full color is carried out immediately after
the gradation correction only for black toner is carried out in the
monochrome control mode and an image of monochrome is formed and output.

[0011] If so, since the gradation correction for full color includes the
gradation correction for black color, the gradation correction for black
color is carried out duplicately within the short span of time, and thus,
toner is uselessly consumed for drawing the adjustment patterns in the
gradation correction. Further, a ratio of an adjustment period of time
with respect to a working period of time of the image forming apparatus,
i.e., downtime, increases, and thus availability of the image forming
apparatus may be degraded. It is noted that such a problem may occur not
only on the gradation correction but also on other drawing parameter
correction such as the position error correction and so forth.

SUMMARY OF THE INVENTION

[0012] According to an embodiment of the present invention, an optical
writing control apparatus controls a light source emitting a light beam
onto a photosensitive member to cause the light source to draw an
electrostatic latent image on the photosensitive member in an image
forming apparatus that develops the electrostatic latent image drawn on
the photosensitive member and forms an image. The optical writing control
apparatus includes a parameter correction part that controls the light
source to cause the light source to emit the light beam and draw a
correction pattern (or adjustment pattern) used for a correction
operation of correcting a parameter value of an image forming mechanism
in the image forming apparatus, detects the correction pattern
transferred onto a surface of a conveyance member based on an output
signal of a sensor that obtains imaging information of the surface of the
conveyance member onto which an image developed on the photosensitive
member is transferred, and corrects the parameter value based on the
detected correction pattern; a progress information storage part that
stores chromatic color progress information indicating a progress having
occurred from when the correction operation for a chromatic color
mechanism of the image forming mechanism corresponding to a chromatic
color image was carried out and achromatic color progress information
indicating a progress having occurred from when the correction operation
for an achromatic color mechanism of the image forming mechanism
corresponding to an achromatic color image was carried out; and a
threshold storage part that stores a necessary threshold used to
determine that the correction operation is necessary and an unnecessary
threshold used to determine that the correction operation is unnecessary
for the chromatic color progress information and the achromatic color
progress information.

[0013] According to another embodiment of the present invention, an
optical writing control apparatus controls a light source emitting a
light beam onto a photosensitive member to cause the light source to draw
an electrostatic latent image on the photosensitive member in an image
forming apparatus that develops the electrostatic latent image drawn on
the photosensitive member and forms an image. A control method of the
optical writing control apparatus includes controlling the light source
to cause the light source to emit the light beam and draw a correction
pattern (or adjustment pattern) used for a correction operation of
correcting a parameter value of an image forming mechanism of the image
forming apparatus, detecting the correction pattern transferred onto a
surface of a conveyance member based on an output signal of a sensor that
obtains imaging information of the surface of the conveyance member onto
which an image developed on the photosensitive member is transferred, and
correcting the parameter value based on the detected correction pattern;
storing chromatic color progress information indicating a progress having
occurred from when the correction operation for a chromatic color
mechanism of the image forming mechanism corresponding to a chromatic
color image was carried out and achromatic color progress information
indicating a progress having occurred from when the correction operation
for an achromatic color mechanism of the image forming mechanism
corresponding to an achromatic color image was carried out; and storing a
necessary threshold used to determine that the correction operation is
necessary and an unnecessary threshold used to determine that the
correction operation is unnecessary for the chromatic color progress
information and the achromatic color progress information.

[0014] Other objects, features and advantages of the present invention
will become more apparent from the following detailed description when
read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a block diagram showing a hardware configuration of an
image forming apparatus according to an embodiment of the present
invention;

[0016]FIG. 2 shows a functional configuration of the image forming
apparatus according to the embodiment of the present invention;

[0017]FIG. 3 shows a configuration of a print engine according to the
embodiment of the present invention;

[0018]FIG. 4 is a plan view showing a configuration of an optical writing
apparatus according to the embodiment of the present invention;

[0019]FIG. 5 is a side sectional view of the configuration of the optical
writing apparatus according to the embodiment of the present invention;

[0020]FIG. 6 is a block diagram showing a control part of the optical
writing apparatus according to the embodiment of the present invention;

[0021]FIG. 7 shows information stored in a reference value storage part
according to the embodiment of the present invention;

[0022]FIG. 8 shows an example of patterns drawn in a position error
correction operation according to the embodiment of the present
invention;

[0023]FIG. 9 shows an example of patterns drawn in a gradation correction
operation according to the embodiment of the present invention;

[0024] FIG. 10 shows an example of patterns drawn in a monochrome position
error correction operation according to the embodiment of the present
invention;

[0025] FIG. 11 shows an example of patterns drawn in a monochrome
gradation correction operation according to the embodiment of the present
invention;

[0026] FIG. 12 shows an example of patterns drawn in a color position
error correction operation according to the embodiment of the present
invention;

[0027]FIG. 13 shows an example of patterns drawn in a color gradation
correction operation according to the embodiment of the present
invention;

[0028]FIG. 14 shows information stored in the writing control part
according to the embodiment of the present invention;

[0029] FIG. 15 shows a method of determining whether it is necessary to
carry out gradation correction operation according to the embodiment of
the present invention;

[0030]FIG. 16 shows a method of determining whether it is necessary to
carry out position error correction operation according to the embodiment
of the present invention;

[0031] FIG. 17 is a flowchart showing an operation for a case where a job
is input in the image forming apparatus according to the embodiment of
the present invention;

[0032]FIG. 18 is a flowchart showing an operation of determining whether
it is necessary to carry out a correction operation according to the
embodiment of the present invention; and

[0033]FIG. 19 is a flowchart showing an operation of determining whether
it is necessary to carry out an operation of adjustment of amounts of
light of a sensor control part according to the embodiment of the present
invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] An embodiment of the present invention has been devised in
consideration of the above-mentioned circumstances, and an object of the
embodiment is to reduce consumption of developer in an operation of
adjustment (or correction) of an optical writing apparatus included in an
image forming apparatus and to shorten downtime.

[0035] Below, with reference to figures, the embodiment of the present
invention will be described in detail. As the embodiment, an image
forming apparatus in a form of an MFP will be described for example. The
image forming apparatus according to the embodiment is an image forming
apparatus of the electrophotographic type, and an object of the
embodiment is to reduce consumption of developer in an operation of
adjustment (or correction) of parameters in an optical writing apparatus
that draws an electrostatic latent image on a photosensitive member
included in an image forming apparatus and to shorten downtime.

[0036]FIG. 1 is a block diagram showing a hardware configuration of the
image forming apparatus according to the embodiment. As shown in FIG. 1,
the image forming apparatus 1 according to the embodiment includes, in
addition to the same configuration as that of an information processing
terminal such as a common server or PC (Personal Computer), an engine
that carries out forming an image. That is, the image forming apparatus 1
is such that a CPU (Central Processing Unit) 10, a RAM (Random Access
Memory) 11, a ROM (Read Only Memory) 12, the engine 13, a HDD (Hard Disk
Drive) 14 and an I/F (Interface) 15 are connected together by a bus 18.
Further, to the I/F 15, an LCD (Liquid Crystal Display) 16 and an
operation part 17 are connected.

[0037] The CPU 10 is an operation part, and controls the entirety of the
image forming apparatus 1. The RAM 11 is a volatile recording medium for
which it is possible to read and write information at high speed, and is
used by the CPU 10 as a work area for processing information. The ROM 12
is a non-volatile recording medium for which only reading information is
possible, and stores a program such as firmware. The engine 13 is a
mechanism that actually carries out forming an image in the image forming
apparatus 1.

[0038] The HDD 14 is a non-volatile recording medium for which reading and
writing of information is possible, and stores an OS (Operating System),
various control programs, application programs and so forth. The I/F 15
connects between the bus 18 and various types of hardware and a
communication network. The LCD 16 is a visual user interface for the user
to check states of the image forming apparatus 1. The operation part 17
is a user interface such as a keyboard, a mouse and so forth for the user
to input information into the image forming apparatus 1.

[0039] In such a hardware configuration, a program stored in a recording
medium such as the ROM 12, the HDD 14 or an optical disk (not shown) is
read into the RAM 11, and the CPU 10 operates according to the program.
Thus, a software control part is provided. Functional blocks of the image
forming apparatus 1 that achieve functions of the image forming apparatus
1 are provided by combination of the software control part and the
hardware.

[0041] The controller 20 includes a main control part 30, an engine
control part 31, an input/output control part 32, an image processing
part 33 and an operation display control part 34. As shown in FIG. 2, the
image forming apparatus 1 has a configuration of an MFP having the
scanner unit 22 and the print engine 26. It is noted that in FIG. 2,
solid arrows represent electric connections and broken arrows represent
flows of paper.

[0042] The display panel 24 acts as an output interface to visually
indicate states/conditions of the image forming apparatus 1, and also
acts as an input interface (operation part) in a form of a touch panel
used when the user directly operates the image forming apparatus 1 or
inputs information into the image forming apparatus 1. The network I/F 28
is an interface to be used by the image forming apparatus 1 to
communicate with another apparatus via a communication network, and an
Ethernet (registered trademark) or USB (Universal Serial Bus) interface
is used there.

[0043] The controller 20 is provided by a combination of software and
hardware. Specifically, the controller 20 is provided by the software
control part provided as a result of a control program such as firmware,
stored in a non-volatile memory (hereinafter simply referred to as a
memory) such as the ROM 12, a non-volatile memory, the HDD 14 or the
optical disk, being loaded onto a non-volatile memory such as the RAM 11,
and the CPU 10 operating according to the control program, and hardware
such as an integrated circuit. The controller 20 acts as a control part
that controls the entirety of the image forming apparatus 1.

[0044] The main control part 30 controls respective parts included in the
controller 20, and gives instructions to the respective parts of the
controller 20. The engine control part 31 acts as a driving part that
controls and drives the print engine 26, the scanner unit 22 and so
forth. The input/output control part 32 inputs signals and instructions
that have been input via the network I/F 28 into the main control part
30. Further, the main control part 30 controls the input/output control
part 32 and accesses another apparatus via the network I/F 28.

[0045] The image processing part 33 generates drawing information based on
printing information included in a printing job that is input, under the
control of the main control part 30. The drawing information is
information that is used by the print engine 26 that acts as an image
forming part to draw an image to be formed in an image forming operation.
Further, the printing information included in the printing job is image
information obtained from being converted by a printer driver installed
in an information processing apparatus such as a PC into such a form that
the image forming apparatus 1 can recognize. The operation display
control part 34 carries out displaying information on the display panel
24 and provides information that is input via the display panel 24 to the
main control part 30.

[0046] In a case where the image forming apparatus 1 acts as a printer,
first the input/output control part 32 receives the printing job via the
network I/F 28. The input/output control part 32 transfers the received
printing job to the main control part 30. After receiving the printing
job, the main control part 30 controls the image processing part 33, and
causes the image processing part 33 to generate the drawing information
based on the printing information included in the printing job.

[0047] After the drawing information is generated by the image processing
part 33, the engine control part 31 carries out forming an image onto
paper conveyed from the paper feeding table based on the drawing
information. That is, the print engine 26 acts as the image forming part.
A document in which the printer engine 26 has formed the image is then
ejected to the paper ejection tray 27.

[0048] In a case where the image forming apparatus 1 acts as a scanner, in
response to an operation made by the user from the display panel or a
scan execution instruction that is input by an external PC or such via
the network I/F 28, the operation display control part 34 or the
input/output control part 32 transfers the scan execution signal to the
main control part 30. The main control part 30 controls the engine
control part 31 based on the received scan execution signal.

[0049] The engine control part 31 drives the ADF 21, and the ADF 21
conveys an original from which imaging information is to be obtained and
which is set on the ADF 21, to the scanner unit 22. The engine control
part 31 drives the scanner unit 22, and the scanner unit 22 obtains
imaging information from the original. Further, in a case where no
original is set on the ADF 21 and an original is directly set on the
scanner unit 22, the scanner unit 22 obtains imaging information from the
original under the control of the engine control part 31. That is, the
scanner unit 22 acts as an imaging part.

[0050] In an imaging operation of obtaining the imaging information from
the original, an imaging device such as a CCD (Charge Coupled Device)
included in the scanner unit 22 optically scans the original, and the
imaging information is generated based on thus-obtained optical
information. The engine control part 33 transfers the imaging information
thus generated by the scanner unit 22 to the image processing part 33.
The image processing part 33 generates image information based on the
imaging information received from the engine control part 31 under the
control of the main control part 30. The image information generated by
the image processing part 33 is stored in a recording medium such as the
HOD 40 included in the image forming apparatus 1. That is, the scanner
unit 22, the engine control part 31 and the image processing part 33 act
as an original reading part in cooperation.

[0051] The image information generated by the image processing part 33 is
stored in the HDD 40 or such, or is transmitted to an external apparatus
via the input/output control part 32 and the network I/F 48 according to
an instruction given by the user. That is, the ADF 21, the scanner unit
22 and the engine control part 31 act as an image inputting part.

[0052] In a case where the image forming apparatus 1 acts as a copier, the
image processing part 33 generates drawing information based on imaging
information that the engine control part 31 has received from the scanner
unit 22 or image information that the image processing part has
generated. Then, based on the drawing information, the same as the
printer operation, the engine control part 31 drives the print engine 26.

[0053] Next, with reference to FIG. 3, the configuration of the print
engine 26 according to the embodiment will be described. The print engine
26 has a configuration that image forming parts 106BK, 106M, 106C and
106Y of the respective colors are arranged along a conveyance belt 105
that is an endless moving part, and is of a so-called tandem type. That
is, along the conveyance belt 105 that conveys paper (recording paper)
separated and fed from a paper feeding tray 101 by a paper feeding roller
102 and a separation roller 103, the plural image forming parts (i.e.,
electrophotographic process parts) 106BK, 106M, 106C and 106Y are
arranged in sequence from the upstream side of the conveyance direction
in the stated order.

[0054] These plural image forming parts 106BK, 106M, 106C and 106Y have a
common inner configuration except for the colors of toner images. The
image forming part 106BK forms a black image; the image forming part 106M
forms a magenta image; the image forming part 106C forms a cyan image;
and the image forming part 106Y forms a yellow image. It is noted that
hereinafter, the image forming part 106BK will be described specifically.
The other image forming parts 106M, 106C and 106Y are similar to the
image forming part 106BK. Therefore, for respective parts/components of
the image forming parts 106M, 106C and 106Y, reference numerals
distinguished by "M" "C" and "Y" are given instead of "BK" given to the
corresponding parts/components of the image forming part 106BK, and
duplicate description will be omitted.

[0055] The conveyance belt 105 is an endless belt wound between a driving
roller 107 that is driven and rotated and a driven roller 108. The
driving roller 107 is driven and rotated by a driving motor (not shown),
and the driving motor, the driving roller 107 and the driven roller 108
act as a driving part that moves the conveyance belt 105.

[0056] When an image is formed, paper 104 is fed in sequence, sheet by
sheet, from the top, from the paper feeding tray 101, and is conveyed to
the first image forming part 106BK by the conveyance belt 105 that is
driven and rotated, as the paper 104 is being attracted by the conveyance
belt 105 because of an electrostatic attraction effect, and a black toner
image is transferred to the conveyed paper 104. That is, the conveyance
belt 105 acts as a conveyance member that conveys the paper to which the
image is transferred.

[0057] The image forming part 106BK includes a photosensitive drum 109BK
as a photosensitive member, and an electrification device 106BK, an
optical writing apparatus 111, a development device 112BK, a
photosensitive member cleaner (not shown), an electricity removal device
113BK and so forth which are arranged around the photosensitive drum
109BK. The optical writing apparatus 111 is configured to emit laser
beams to the respective ones of the photosensitive drums 109BK, 109M,
109C and 109Y (hereinafter generally referred to as photosensitive drums
109).

[0058] When an image is formed, an outer circumferential surface of the
photosensitive drum 109BK is uniformly electrified by the electrification
device 110BK in the dark, then writing is carried out on the outer
circumferential surface of the photosensitive drum 109BK by the laser
beam corresponding to the black image from the optical writing apparatus
111, and thus an electrostatic latent image is formed on the outer
circumferential surface of the photosensitive drum 109BK. The development
device 112BK develops the electrostatic latent image by black toner to
visualize it, and thus, the black toner image is formed on the
photosensitive drum 109BK.

[0059] The toner image is transferred to the paper 104 by the function of
a transfer device 115BK at a position (transfer position) at which the
paper 104 on the conveyance belt 105 comes into contact with the
photosensitive drum 109BK. By the transfer, the black toner image is
formed on the paper 104. After the transfer of the toner image is thus
finished, residual unnecessary toner on the outer circumferential surface
of the photosensitive drum 109BK is wiped off by the photosensitive
member cleaner, then, the electricity is removed from the photosensitive
drum 109BK by the electricity removal device 113b, and the photosensitive
drum 109BK is on standby for the next forming of an image.

[0060] The paper 104 onto which the black toner image has been thus
transferred by the image forming part 106BK is conveyed to the next image
forming part 106M by the conveyance belt 105. In the image forming part
106M, by the same process as that in the image forming part 106BK, a
magenta toner image is formed on the photosensitive drum 109M and the
toner image is then transferred and superposed on the black image having
been formed on the paper 104.

[0061] The paper 104 is further transferred to the next image forming
parts 106C and 106Y, a cyan toner image formed on the photosensitive drum
109C and a yellow toner image formed on the photosensitive drum 109Y are
transferred and superposed on the paper 104 in the same operation. Thus,
a full color image is formed on the paper 104. The paper 104 on which the
full color image has been thus formed is removed from the conveyance belt
105, the full color image is fixed onto the paper 104 by a fixing device
116, and then, the paper 104 is ejected to the outside of the image
forming apparatus 1.

[0062] In the image forming apparatus 1, an error in distances between the
axes of the photosensitive drums 109BK, 109M, 109C and 109Y, an error in
parallelism between the photosensitive drums 109BK, 109M, 109C and 109Y,
an error of setting of a deflection mirror in the optical writing
apparatus 111, a timing error in writing of electrostatic latent images
to the photosensitive drums 109BK, 109M, 109C and 109Y, and so forth, may
result in the toner images of the respective colors which are to be
superposed at a position not being superposed at the position actually,
and cause a position error between the respective colors.

[0063] Further, by the same causes, on the paper to which an image is to
be transferred, the image may be transferred to an area other than an
area to which the image is to be transferred. As factors causing such a
position error, mainly a skew, an error in registration in the sub-scan
direction, an error in magnification in the main scan direction, an error
in registration in the main scan direction, and so forth are known.
Further, expansion or contradiction of the conveyance belt 105 caused by
a change in temperature in the image forming apparatus 1 or aging is
known.

[0064] Further, in the image forming apparatus 1, density gradation or
density balance between the respective colors of transferred images
formed on the photosensitive drums 109BK, 109M, 109C and 109Y may not be
in desired states. This is because development characteristics may vary
because of conditions of temperature, humidity and so forth of the
environment in which the image forming apparatus 1 operates.

[0065] In order to correct such a position error and density gradation, a
pattern detection sensor 117 is provided. The pattern detection sensor
117 is an optical sensor to read position error correction patterns and
gradation correction patterns (hereinafter generally referred to as
correction patterns) transferred onto the conveyance belt 105 from the
photosensitive drums 109BK, 109M, 109C and 109Y, and includes light
emission devices that irradiate the correction patterns drawn on the
surface of the conveyance belt 105 and light reception devices that
receive reflection light from the correction patterns.

[0066] The pattern detection sensor 117 is supported by the same substrate
along a direction perpendicular to the conveyance direction of the
conveyance belt 105 on the downstream side of the photosensitive drums
109BK, 109M, 109C and 109Y as shown in FIG. 3. Details of the pattern
detection sensor 117 and a method of position error correction and
gradation correction will be described later. It is noted that each of
position error correction and gradation correction is correction of
parameters concerning the operation of forming electrostatic latent
images on the photosensitive drums 109BK, 109M, 109C and 109Y and
developing them, i.e., the operation of drawing images, and thus,
hereinafter, will be generally referred to as drawing parameter
correction.

[0067] A belt cleaner 118 is provided for removing toner of the correction
patterns drawn on the conveyance belt 105 in the drawing parameter
correction for preventing paper 104 conveyed by the conveyance belt 105
from being stained. The belt cleaner 118 is a cleaning blade that is
pressed onto the conveyance belt 105 on the downstream side with respect
to the pattern detection sensor 117 and on the upstream side with respect
to the photosensitive drums 109, as shown in FIG. 3, and is a developer
removal part that scrapes toner adhering to the surface of the conveyance
belt 105.

[0068] Further, the belt cleaner 118 according to the embodiment has a
function of collecting toner adhering to the conveyance belt 105 by
applying a bias voltage. By applying the voltage having a polarity
reverse to that of electric charge of the toner, it is possible to remove
the toner adhering to the conveyance belt 105 and cause the toner to
attract to the belt cleaner 118.

[0069] It is noted that in a case where the electric charge of the toner
is such that positive and negative polarities are mixed, the belt cleaner
118 oscillates the bias voltage between the positive and negative
polarities. Thereby, it is possible to remove the toner adhering to the
conveyance belt 105 and cause the toner to attract to the belt cleaner
118 whether the toner has the positive or negative polarity.

[0070] Next, the optical writing apparatus 111 according to the embodiment
will be described. FIG. 4 is a plan view of the optical writing apparatus
111 according to the embodiment viewed from the top. FIG. 5 is a
sectional view of the optical writing apparatus 111 according to the
embodiment viewed from the side. As shown in FIGS. 4 and 5, the laser
beams for writing to the photosensitive drums 109BK, 109M, 109C and 109Y
of the respective colors are emitted by light source apparatuses 281BK,
281M, 281C and 281Y which act as light sources (hereinafter, generally
referred to as light source apparatuses 281). It is noted that the light
source apparatuses 281 according to the embodiment include semiconductor
lasers, collimator lenses, slits, prisms, cylinder lenses and so forth.
In FIG. 4, SD denotes a scan direction.

[0071] The laser beams emitted by the light source apparatuses 281 are
reflected by a reflection mirror (or deflection mirror) 280. The
respective laser beams are led to respective mirrors 282BK, 282M, 282C
and 282Y (hereinafter, generally referred to as 282) by optical systems
such as fθ lenses (not shown), and are then caused to scan the
surfaces of the respective photosensitive drums 109BK, 109M, 109C and
109Y by subsequent optical systems.

[0072] The reflection mirror 280 is a polygon mirror of a hexahedron, and
can cause the laser beam to scan for a line of the main scan direction
with each surface of the polygon mirror. The optical writing apparatus
111 according to the embodiment writes to the four different
photosensitive drums simultaneously with a compact configuration, in
comparison to a system of scanning by using only one reflection surface,
according to a system that the four light source apparatuses 281BK, 281M,
281C and 281Y are divided into two groups each corresponding to two
colors of the light source apparatuses and scanning is carried out by
using different reflection surfaces of the reflection mirror 280.

[0073] Further, horizontal synchronization detection sensors 283 are
provided near the positions from which scanning is started, in ranges
scanned by the laser beams with the reflection mirror 280. The laser
beams emitted by the light source apparatuses 281 are incident on the
horizontal synchronization detection sensors 283, thereby the timings of
starting the main scan lines are detected, and thus, the light source
apparatuses 281 and the reflection mirror 280 are synchronized together.

[0074] Next, control blocks of the optical writing apparatus 111 according
to the embodiment will be described with reference to FIG. 6. FIG. 6
shows a functional configuration of an optical writing apparatus control
part 120 that controls the optical writing apparatus 111, and a
connection with the light source apparatuses 281 and the pattern
detection sensor 117.

[0075] As shown in FIG. 6, the optical writing apparatus control part 120
according to the embodiment includes a writing control part 121, a count
part 122, a sensor control part 123, a correction value calculation part
124, a reference value storage part 125 and a correction value storage
part 126. It is noted that the optical writing apparatus 111 according to
the embodiment includes an information processing mechanism such as a CPU
10, a RAM 11, a ROM 12, a HDD 14 and so forth described with reference to
FIG. 1, and the optical writing apparatus control part 120 shown in FIG.
6 is configured as a result of, the same as the controller 20 of the
image forming apparatus 1, a control program stored in the ROM 12 or the
HDD 14 being loaded onto the RAM 12, and an operation being carried out
under the control of the CPU 10 that executes the control program.

[0076] The writing control part 121 is a light source control part that
controls the light source apparatuses 281 according to synchronization
detection signals provided by the horizontal synchronization sensors 283
based on image information that is input from the engine control part 31
of the controller 20. Further, the writing control part 121 drives the
light source apparatuses 281 for drawing the correction patterns in the
above-described drawing parameter correction process in addition to
driving the light source apparatuses 281 based on the image information
that is input from the engine control part 31. Correction values that are
generated as a result of the position error correction process of the
drawing parameter correction process are stored in the correction value
storage part 126 as position error correction values, and the writing
control part 121 corrects timings of driving the light source apparatuses
281 based on the position error correction values stored in the
correction value storage part 126.

[0077] Further, the writing control part 121 has a function of obtaining
the detection signals from the horizontal synchronization detection
sensors 283, and synchronizing with rotation of the reflection mirror 280
as described above with reference to FIG. 4. Further, the writing control
part 121 functions as a voltage control part that controls, when
developing the electrostatic latent images formed on the photosensitive
drums 109 by using toner that is developer, voltages (hereinafter,
referred to as bias voltages) to be applied between the photosensitive
drums 109BK, 109M, 109C and 109Y and the development devices 112BK, 112M,
112C and 112Y. Also correction values generated by the gradation
correction of the drawing parameter correction are stored in the
correction value storage part 126 as gradation correction values, and the
writing control part 121 corrects the bias voltages (i.e., development
biases) based on the gradation correction values stored in the correction
value storage part 126.

[0078] The count part 122 starts counting at the same time when the
writing control part 121 controls the light source apparatus 281BK and
starts exposure of the photosensitive drum 109BK. The count part 122
stops the counting as a result of the sensor control part 123 detecting
the position error correction pattern based on the output signal of the
pattern detention sensor 117. Thereby, the count part 122 functions as a
detection time period count part that counts (i.e., measures) a detection
period of time in the position error correction process from when the
writing control part 121 controls the light source apparatus 281BK and
starts exposure of the photosensitive drum 109BK up to when the pattern
detection sensor 117 detects the position error correction pattern.
Hereinafter, the count value (i.e., measured value) is referred to as a
writing start count value. Further, the count part 122 counts (i.e.,
measures) timings of detecting patterns that are successively drawn in
the position error correction process for correcting position errors of
toner images of the respective colors. Hereinafter, these count values
are referred to as drum interval count values.

[0079] The sensor control part 123 is a control part that controls the
pattern detection sensor 117, and, as described above, is an arrival
determination part that determines, based on the output signal of the
pattern detection sensor 117, that the position error correction patterns
formed on the conveyance belt 105 have arrived at the position of the
pattern detection sensor 123. Further, the sensor control part 123 is a
gradation determination part that determines the densities of the
gradation correction patterns formed on the conveyance belt 105, based on
the output signal of the pattern detection sensor 117.

[0080] The sensor control part 123 inputs a detection signal to the count
part 122 when determining that the position error correction patterns
have arrived at the position of the pattern detection sensor 117 as
described above. Further, the sensor control part 123 inputs a signal
indicating determined densities to the correction value calculation part
124 when determining the densities of the gradation correction patterns.
That is, the sensor control part 123 acts as an image detection part.

[0081] Further, the sensor control part 123 has a function of controlling
the pattern detection sensor 117, and adjusting the amounts of light of
the light emission devices included in the pattern detection sensor 117.
That is, the pattern detection sensor 117 acts as a light amount
adjustment part. When adjusting the amounts of light of the light
emission devices, the pattern detection sensor 117 drives the light
emission devices with predetermined power, and irradiates the conveyance
belt 105 in a state of a white background on which nothing has been
drawn, for example. It is noted that a toner mark or such formed on the
conveyance belt 105 may be used in the adjustment of the amounts of light
of the light emission devices. Then, based on the output signals of the
light reception devices having received reflection light from the white
background of the conveyance belt 105, emission amounts of light of the
light emission devices are determined and adjusted.

[0082] For example, when the output signals of the light reception devices
are lower than a target value, the sensor control part 123 carries out
the same process after increasing the driving power of the light emission
devices. On the other hand, when the output signals of the light
reception devices are higher than the target value, the sensor control
part 123 carries out the same process after lowering the driving power of
the light emission devices. As a result of the sensor control part 123
repeating the processes, the driving power of the light emission devices
are adjusted so that the output signals of the light reception devices
become the target value, and as a result, the emission amounts of light
of the light emission devices are adjusted to appropriate levels.

[0083] As a result of the amounts of light reflected by the conveyance
belt 105 being thus adjusted to a predetermined target value, S/N ratios
of the light reception device are improved, and thus, it is possible to
detect the position error correction patterns with high accuracy. This
process of adjusting the amounts of light may be carried out when the
position error correction process is carried out.

[0084] The correction value calculation part 124 calculates the correction
values based on position error correction reference values stored in the
reference value storage part 125 based on the count results of the count
part 122. That is, the correction value calculation part 124 acts as a
reference value obtaining part and a correction value calculation part.
FIG. 7 shows example of the reference values stored in the reference
value storage part 125. As shown in FIG. 7, in the reference value
storage part 125, a writing start timing reference value, drum interval
reference values and density gradation reference values are stored.

[0085] The writing start timing reference value is a reference value for
the period of time from when the writing control part 121 controls the
light source apparatus 281BK and starts exposure of the photosensitive
drum 109BK up to when the pattern detection sensor 117 detects the
position error correction pattern. That is, the correction value
calculating part 124 compares the writing start count value of the count
values of the count part 122 with the writing start timing reference
value, and calculates the correction value for the error therebetween.

[0086] The drum interval reference values are reference values for the
detection timings for detecting the respective ones of the patterns drawn
successively as described above. That is, the correction value
calculating part 124 compares the drum interval count values of the count
values of the count part 122 with the drum interval reference values, and
calculates the correction values for the errors therebetween.

[0087] The density gradation reference values are reference values for
densities of respective ones of the gradation correction patterns drawn
for the respective colors described above. That is, the correction value
calculating part 124 compares the densities of the gradation correction
patterns determined by the sensor control part 123 with the density
gradation reference values, and calculates the correction values for the
errors therebetween. The thus-calculated correction values are stored in
the correction value storage part 126. As a result of the correction
values being stored in the correction value storage part 126, the writing
control part 121 reads the correction values, and drives the light source
apparatuses 281 and the apparatuses that generate the development biases
(i.e., the bias voltages).

[0088] It is noted that the optical writing apparatus 111 according to the
embodiment has, in addition to the functions shown in FIG. 6, a function
of controlling the driving roller 107 that rotates the conveyance belt
105 and a function of controlling the belt cleaner 118.

[0089] Next, with reference to FIG. 8, the position error correction
operation according to the embodiment will be described. FIG. 8 shows
marks (hereinafter, referred to as position error correction marks) drawn
on the conveyance belt 105 by the light source apparatuses 281 that are
controlled by the writing control part 121 in the position error
correction operation according to the embodiment. As shown in FIG. 8, the
position error correction marks 400 according to the embodiment are such
that plural (in the embodiment, three) rows 401 of position error
correction patterns that include various patterns arranged in the
sub-scan direction are arranged in the main scan direction. It is noted
that in FIG. 8, MSD denotes the main scan direction, and SSD denotes the
sub-scan direction. It is noted that in FIG. 8, solid lines denote
patterns drawn by the photosensitive drum 109BK; dotted lines denote
patterns drawn by the photosensitive drum 109Y; broken lines denote
patterns drawn by the photosensitive drum 109C; and dashed-dotted lines
denote patterns drawn by the photosensitive drum 109M.

[0090] As shown in FIG. 8, the pattern detection sensor 117 has plural (in
the embodiment, three) sensor devices 170 in the main scan direction, and
the respective rows 401 of position error correction patterns are drawn
on positions corresponding to the respective sensor devices 170. Thereby,
the optical writing apparatus control part 120 can detects the patterns
at the plural positions in the main scan direction, and accuracy in the
position error correction operation can be improved as an average of the
respective ones is calculated.

[0091] As shown in FIG. 8, the rows 401 of the position error correction
patterns include start position correction patterns 411 and drum interval
correction patterns 412. Further, as shown in FIG. 8, the drum interval
correction patterns 412 are drawn repetitiously. The start position
correction patterns 411 are patterns drawn for counting the writing start
count value. Further, the start position correction patterns 411 are used
by the sensor control part 123 to correct the detection timing of
detecting the drum interval correction patterns 412.

[0092] The start position correction patterns 411 according to the
embodiment are lines drawn by the photosensitive drum 109BK, and lines
parallel to the main scan direction, as shown in FIG. 8. In start
position correction by using the start position correction patterns 411,
the optical writing apparatus control part 120 carries out a correction
operation for the writing start timing based on reading signals from the
start position correction patterns 411 provided by the pattern detection
sensor 117. That is, the writing start timing reference value stored in
the reference storage part 125 is a value of reference for a period of
time from when the light source apparatus 281BK starts drawing of the
black patterns of the start position correction patterns 411 by the
photosensitive drum 109BK up to when the drawn black patterns are read by
the pattern detection sensor 117 and the sensor control part 123 detects
the patterns.

[0093] The drum interval correction patterns 412 are patterns drawn for
counting the above-described drum interval count values. As shown in FIG.
8, the drum interval correction patterns 412 include sub-scan direction
correction patterns 413 and main scan direction correction patterns 414.
The optical writing apparatus control part 120 corrects respective
position errors in the sub-scan direction of the photosensitive drums
109BK, 109M, 109C and 109Y based on reading signals from the sub-scan
direction correction patterns 413 provided by the pattern detection
sensor 117, and corrects respective position errors in the main scan
direction of the respective photosensitive drums 109 based on reading
signals from the main scan direction correction patterns 414 provided by
the pattern detection sensor 117.

[0094] That is, the drum interval reference values stored in the reference
value storage part 125 are values of reference for periods of time from
when the light source apparatuses 281 start drawing of the drum interval
correction patterns 412 under the control of the writing control part 121
up to when the respective lines included in the drawn drum interval
correction patterns are read by the pattern detection sensor 117 and the
sensor control part 123 detects the lines of the patterns. Thus, in the
position error correction operation according to the embodiment, the
writing control part 121, the count part 122, the sensor control part 123
and the correction value calculation part 124 cooperate together and
function as a parameter correction part.

[0095] Next, with reference to FIG. 9, the gradation correction operation
according to the embodiment will now be described. FIG. 9 shows marks
(hereinafter, referred to as gradation correction marks) drawn on the
conveyance belt 105 by the light source apparatuses 281 that are
controlled by the writing control part 121 in the gradation correction
operation according to the embodiment. As shown in FIG. 9, the gradation
correction marks 500 include black gradation patterns 501, yellow
gradation patterns 502, magenta gradation patterns 503 and cyan gradation
patterns 504.

[0096] The gradation patterns of each color included in the gradation
correction patterns 500 include four square patterns having different
densities, and the square patterns are arranged in the sub-scan direction
in the order of the densities. Then, the gradation patterns of the
respective colors are arranged in the sub-scan direction in the stated
order of black, yellow, magenta and cyan. It is noted that as shown in
FIG. 9, the gradation correction patterns 500 according to the embodiment
are drawn at positions corresponding to the center sensor device of the
three sensor devices 170 included in the pattern detection sensor 117.
Further, in FIG. 9, the number of lines included in the hatching included
in each square pattern represents the density of the respective one of
the square patterns.

[0097] In the gradation correction using the gradation correction marks
500 shown in FIG. 9, the correction value calculation part 124 obtains
from the sensor control part 123 information indicating densities based
on reading signals from the gradation patterns of the respective colors
provided by the pattern detection sensor 117, and carries out a
correction operation for the bias voltages (development biases). That is,
the density gradation reference values stored in the reference value
storage part 125 are values of reference for the respective densities of
the four square patterns having the different densities included in the
gradation patterns of each color. Thus, in the gradation correction
operation according to the embodiment, the writing control part 121, the
sensor control part 123 and the correction value calculation part 124
cooperate and function as the parameter correction part.

[0098] In the image forming apparatus 1 and the drawing parameter
correction operation according to the embodiment, determination as to
which one is to be carried out from among drawing parameter correction
only corresponding to a monochrome image forming mechanism, drawing
parameter correction corresponding to a color image forming mechanism and
drawing parameter correction corresponding to a full color image forming
mechanism is optimized, and thus, reduction of the toner consumption
amount and reduction of downtime of the image forming apparatus 1 are
achieved. For this purpose, the optical writing apparatus control part
120 according to the embodiment, in addition to the drawing parameter
correction operation for full color as described with reference to FIGS.
8 and 9, the drawing parameter correction operation only for monochrome
images and the drawing parameter correction operation for color images
are carried out. Then, when a correction operation for the drawing
parameters is to be carried out, it is determined which of the
above-mentioned three types of correction operations is to be carried
out. Below, the correction operation for the drawing parameters according
to the embodiment will be described.

[0100] As shown in FIG. 10, the monochrome position error correction marks
410 only includes the start position correction patterns 411 from among
the position error correction marks 400 described above with reference to
FIG. 8. Thus, only the start position correction operation of the
above-described position error correction operation is carried out in the
position error correction only for monochrome images.

[0101] As shown in FIG. 11, the monochrome gradation correction marks 510
only includes the black gradation patterns 501 from among the gradation
correction marks 500 described above with reference to FIG. 9. Thus, only
adjustment of the bias voltage (i.e., the developing bias) to be applied
to the photosensitive drum 109BK of the above-described gradation
correction operation is carried out in the gradation correction only for
monochrome images.

[0102] As shown in FIG. 12, the color position error correction marks 420
only includes the drum interval correction patterns 412 from among the
position error correction marks 400 described above with reference to
FIG. 8. Thus, only the drum interval correction operation of the
above-described position error correction operation is carried out in the
position error correction for color images of the colors other than
black.

[0103] It is noted that as shown in FIG. 12, the drum interval correction
patterns 412 include the patterns formed by the photosensitive drum
109BK. However, in the position error correction operation, the
correction of the start position by using the start position correction
patterns 411 such as those shown in FIG. 10 corresponds to monochrome
correction, and the correction of only drum intervals regardless of the
start position, as described with reference to FIG. 12, corresponds to
color correction.

[0104] As shown in FIG. 13, the color gradation correction marks 520 only
include the gradation patterns other than the black gradation patterns
501 from among the gradation correction marks 500 described above with
reference to FIG. 9. Thus, only adjustment of the bias voltages (i.e.,
the developing biases) to be applied to the photosensitive drums other
than the photosensitive drum 109BK of the above-described gradation
correction operation is carried out in the gradation correction for color
images of the colors other than black.

[0105] Thus, in the optical writing apparatus control part 120 according
to the embodiment, it is possible to carry out, in a switching manner,
one of the three types of correction operations respectively
corresponding to the full color, monochrome and color, in the position
error correction and the gradation correction. Next, the switching
between the three types of correction operations will be described.

[0106]FIG. 14 shows information stored by the writing control part 121
for switching the above-mentioned three types of correction operations.
The writing control part 121 according to the embodiment stores
information of "output number of sheets count values" and "correction
operation switching thresholds" as shown in FIG. 14.

[0107] Further, the "output number of sheets count values" includes, as
shown in FIG. 14, respective count values of "after monochrome position
error correction execution", "after color position error correction
execution", "after monochrome gradation correction execution" and "after
color gradation correction execution". The count value of "after
monochrome position error correction execution" indicates the number of
sheets that have been output (i.e., printed) in the image forming
apparatus 1 since the correction by drawing the monochrome position error
correction marks 410 shown in FIG. 10 was carried out last. Therefore,
when the monochrome position error correction is carried out, the count
value of "after monochrome position error correction execution" shown in
FIG. 14 is reset.

[0108] The count value of "after color position error correction
execution" indicates the number of sheets that have been output (i.e.
printed) in the image forming apparatus 1 since the correction by drawing
the color position error correction marks 420 shown in FIG. 12 was
carried out last. Therefore, when the color position error correction is
carried out, the count value of "after color position error correction
execution" shown in FIG. 14 is reset. It is noted that when the
correction is carried out by drawing the position error correction marks
400 shown in FIG. 8, it can be said that both the monochrome position
error correction and the color position error correction are carried out,
and thus, both the count values of "after monochrome position error
correction execution" and "after color position error correction
execution" shown in FIG. 14 are reset.

[0109] The count value of "after monochrome gradation correction
execution" indicates the number of sheets that have been output (i.e.
printed) in the image forming apparatus 1 since the correction by drawing
the monochrome gradation correction marks 510 shown in FIG. 11 was
carried out last. Therefore, when the monochrome gradation correction is
carried out, the count value of "after monochrome gradation correction
execution" shown in FIG. 14 is reset.

[0110] The count value of "after color gradation correction execution"
indicates the number of sheets that have been output (i.e. printed) in
the image forming apparatus 1 since the correction by drawing the color
gradation correction marks 520 shown in FIG. 13 was carried out last.
Therefore, when the color gradation correction is carried out, the count
value of "after color gradation correction execution" shown in FIG. 14 is
reset. It is noted that when the correction is carried out by drawing the
gradation correction marks 500 shown in FIG. 9, it can be said that both
the monochrome gradation correction and the color position gradation
correction are carried out, and thus, both the count values of "after
monochrome gradation correction execution" and "after color gradation
correction execution" shown in FIG. 14 are reset.

[0111] The above-mentioned count values of "after monochrome position
error correction execution" and "after monochrome gradation correction
execution" are achromatic color progress information indicating a
progress having occurred in the image forming apparatus 1 since the
correction operation was carried out last for the mechanism of forming
and outputting achromatic images, i.e., the photosensitive drum 109BK.
Further, the above-mentioned count values of "after color position error
correction execution" and "after color gradation correction execution"
are chromatic color progress information indicating a progress having
occurred in the image forming apparatus 1 since the correction operation
was carried out last for the mechanism of forming and outputting
chromatic images, i.e., the photosensitive drums 109M, 109C and 109Y.
Thus, the writing control part 121 functions as a progress information
storage part.

[0112] It is noted that as mentioned above, even in a case of chromatic
color position error correction, i.e., in a case where the correction
patterns of FIG. 12 are drawn and the correction is carried out, the
patterns by the photosensitive drum 109BK are drawn. However, this
operation is necessary to correct the parameter values of the drum
intervals, and thus, the case where the correction patterns of FIG. 12
are drawn and the correction is carried out can be referred to as
chromatic color position error correction because this case is not the
case where only the photosensitive drum 109BK is directed to as the case
of drawing the patterns shown in FIG. 10. Further, because the start
position correction patterns 411 that are directed only to the
photosensitive drum 109BK are not included in the correction patterns of
FIG. 12, the case where the correction patterns of FIG. 12 are drawn and
the correction is carried out is not to be referred to as full color
position error correction but to be referred to as color position error
correction.

[0113] The "correction operation switching thresholds" shown in FIG. 14
includes "position error correction execution necessary threshold",
"position error correction execution unnecessary threshold", "gradation
correction execution necessary threshold" and "gradation correction
execution unnecessary threshold". The "position error correction
execution necessary threshold" and the "position error correction
execution unnecessary threshold" are thresholds for the count values of
"after monochrome position error correction execution" and "after color
position error correction execution", and are thresholds for determining
that execution of the position error correction is necessary and for
determining that execution of the position error correction is
unnecessary, respectively.

[0114] On the other hand, the "gradation correction execution necessary
threshold" and the "gradation correction execution unnecessary threshold"
are thresholds for the count values of "after monochrome gradation
execution" and "after color gradation correction execution", and are
thresholds for determining that execution of the gradation correction is
necessary and for determining that execution of the gradation correction
is unnecessary, respectively. Thus, the writing control part 121
functions as a threshold storage part.

[0115] According to the embodiment, the "position error correction
execution necessary threshold" is "120 sheets", and the "position error
correction execution unnecessary threshold" is "100 sheets". Further, the
"gradation correction execution necessary threshold" is "200 sheets", and
the "gradation correction execution unnecessary threshold" is "180
sheets". That is, differences exist between the respective correction
execution necessary thresholds and correction execution unnecessary
thresholds. Determinations are made when the above-mentioned count values
are between the correction execution necessary thresholds and correction
execution unnecessary thresholds as described below.

[0116] FIG. 15 shows determinations made in cases where the
above-mentioned count values are between the correction execution
necessary threshold and correction execution unnecessary threshold. In
FIG. 15, the count values of "after monochrome gradation correction
execution" and "after color gradation correction execution" are arranged
in a form of a matrix based on the above-mentioned "gradation correction
execution necessary threshold" and "gradation correction execution
unnecessary threshold", and determination results for the respective
count values are described in respective cells.

[0117] For example, in a case where each of both the count values of
"after monochrome gradation correction execution" and "after color
gradation correction execution" is equal to or more than 200 sheets, the
count value becomes equal to or more than the thresholds for the
gradation correction being necessary for both monochrome and color, and
thus, full color gradation correction is carried out (cell (a) of FIG.
15).

[0118] On the other hand, in a case where the count value of "after
monochrome gradation correction execution" is equal to or more than 200
sheets and the count value of "after color gradation correction
execution" is less than 180 sheets, the monochrome gradation correction
is necessary but the color gradation correction is unnecessary, and thus,
the monochrome gradation correction is carried out (cell (c) of FIG. 15).

[0119] In a case where the count value of "after monochrome gradation
correction execution" is less than 180 sheets and the count value of
"after color gradation correction execution" is equal to or more than 200
sheets, the monochrome gradation correction is unnecessary but the color
gradation correction is necessary, and thus, the color gradation
correction is carried out (cell (g) of FIG. 15).

[0120] In a case where each of both the count values of "after monochrome
gradation correction execution" and "after color gradation correction
execution" is less than 180 sheets, none of the monochrome gradation
correction and the color gradation correction is necessary, and thus, no
correction (i.e., no adjustment) is carried out (cell (i) of FIG. 15).

[0121] Here, a case where the count value of "after monochrome gradation
correction execution" is equal to or more than 180 sheets and less than
200 sheets will be described. In this case, because the count value has
not become equal to or more than the above-mentioned gradation correction
execution necessary threshold, and thus, in principle, the monochrome
gradation correction is not carried out. As shown in FIG. 15, cells (e)
and (f), when the count value of "after color gradation correction
execution" is less than 200 sheets, also execution of the color gradation
correction is not determined to be necessary, and thus, no correction
(i.e., no adjustment) is carried out the same as the above-mentioned cell
(i). On the other hand, when the count value of "after color gradation
correction execution" is equal to or more than 200 sheets, at least the
color gradation correction is carried out. At this time, if only the
color gradation correction were carried out, the count value of "after
monochrome gradation correction execution" would become equal to or more
than the 200 sheets in a case where, after that, for example, a job of
forming and outputting on the order of 20 sheets will be input and then a
job of forming and outputting a monochrome image or images will be input
within a short span of time. In this case, as a result, the monochrome
gradation correction would be carried out within the short span of time
after the color gradation correction would be carried out.

[0122] According to the embodiment, as shown in FIGS. 11 and 13, the
monochrome gradation correction and the color gradation correction can be
carried out separately. Therefore, even if the monochrome gradation
correction and the color gradation correction would be thus carried out
within a short span of time, useless toner consumption does not occur.
However, a total time of the case where the monochrome gradation
correction and the color gradation correction would be separately carried
out would become longer than a case where the full color gradation
correction is carried out once by drawing the gradation correction marks
500 shown in FIG. 9, because of overhead or such required when starting
the correction (i.e., adjustment) operations. As a result, downtime in
the image forming apparatus 1 would be increased.

[0123] In order to avoid such adverse effect, according to the embodiment,
in a case where the count value "after monochrome gradation correction
execution" is equal to or more than 180 sheets and less than 200 sheets,
that is, in a case where the count value is between the correction
execution unnecessary threshold and the correction execution necessary
threshold (hereinafter, referred to as a correction execution
necessary/unnecessary undetermined range), and also, the count value
"after color gradation correction execution" is equal to or more than 200
sheets, that is, equal to or more than the correction execution necessary
threshold, it is determined that it is immediately before also execution
of the monochrome gradation correction will become necessary. Therefore,
in this case, the full color gradation correction is carried out which
includes not only the gradation correction only for color but also the
monochrome gradation correction (see cell (d) of FIG. 15).

[0124] In other words, according to the embodiment, in a case where the
count value of "after color gradation correction execution" is equal to
or more than 200 sheets, the color gradation correction is carried out in
principle. However, in a case where further the count value "after
monochrome gradation correction execution" is equal to or more than 180
sheets and less than 200 sheets (see cell (d) of FIG. 15), the full color
gradation correction is carried out instead of the color gradation
correction. Thereby, it is possible to avoid a case where the monochrome
gradation correction would be carried out within a short span of time
after the color gradation correction would be carried out and thus
downtime of the image forming apparatus 1 would be increased.

[0125] Similarly, in a case where the count value of "after color
gradation correction execution" is in the correction execution
necessary/unnecessary undetermined range, the color gradation correction
is not carried out in principle (cells (e), (h) of FIG. 15). However, in
a case where further the count value "after monochrome gradation
correction execution" becomes equal to or more than the correction
execution necessary threshold and thus it is determined that execution of
the monochrome gradation correction is necessary, not only the monochrome
gradation correction but the full color gradation correction is carried
out, because a likelihood that the color gradation correction would be
carried out within a short span of time after that is high (cell (b) of
FIG. 15).

[0126]FIG. 16 shows determinations as to whether the position error
correction is necessary, the same as FIG. 15 that shows the
determinations as to whether the gradation correction is necessary. In
FIG. 16, the count values of "after monochrome position error correction
execution" and "after color position error correction execution" are
arranged in a form of a matrix based on the above-mentioned "position
error correction execution necessary threshold" and "position error
correction execution unnecessary threshold", and determination results
for the respective count values are described in respective cells.

[0127] As shown in FIG. 16, the same as the case of the gradation
correction of FIG. 15, in a case where each of both the count values of
"after monochrome position error correction execution" and "after color
position error correction execution" is equal to or more than 120 sheets
("position error correction execution necessary threshold"), the count
value becomes equal to or more than the thresholds for the position error
correction being necessary for both monochrome and color, and thus, full
color position error correction is carried out (cell (a) of FIG. 16).

[0128] In a case where the count value of "after monochrome position error
correction execution" is equal to or more than 120 sheets ("position
error correction execution necessary threshold") and the count value of
"after color position error correction execution" is less than 100
("position error correction execution unnecessary threshold") sheets, the
monochrome position error correction is necessary but the color position
error correction is unnecessary, and thus, the monochrome position error
correction is carried out (cell (c) of FIG. 16).

[0129] In a case where the count value of "after monochrome position error
correction execution" is less than 100 sheets ("position error correction
execution unnecessary threshold") and the count value of "after color
position error correction execution" is equal to or more than 120 sheets
("position error correction execution necessary threshold"), the
monochrome position error correction is unnecessary but the color
position error correction is necessary, and thus, the color position
error correction is carried out (cell (g) of FIG. 16).

[0130] In a case where each of both the count values of "after monochrome
position error correction execution" and "after color position error
correction execution" is less than 100 sheets ("position error correction
execution unnecessary threshold"), none of the monochrome position error
correction and the color position error correction is necessary, and
thus, no correction (i.e., no adjustment) is carried out (cell (i) of
FIG. 16). It is noted that in the case of position error correction, the
monochrome position error correction is the start position correction and
the color position error correction is the drum interval correction as
mentioned above.

[0131] Further, for example, when the count value of "after color position
error correction execution" is equal to or more than the "position error
correction execution necessary threshold" (i.e., 120 sheets) and the
count value of "after monochrome position error correction execution" is
in the "correction execution necessary/unnecessary undetermined range"
(i.e., equal to or more than 100 sheets and less than 120 sheet), the
full color position error correction that includes not only the position
error correction only for color, i.e., the drum interval correction, but
also the monochrome position error correction, i.e., the start position
correction, is carried out (cell (d) of FIG. 16).

[0132] Similarly, when the count value of "after monochrome position error
correction execution" is equal to or more than the "position error
correction execution necessary threshold" (i.e., 120 sheets) and the
count value of "after color position error correction execution" is in
the "correction execution necessary/unnecessary undetermined range"
(i.e., equal to or more than 100 sheets and less than 120 sheets), the
full color position error correction that includes not only the position
error correction only for monochrome, i.e., the start position
correction, but also the position error correction for color, i.e., the
drum interval correction, is carried out (cell (b) of FIG. 16). By the
process, the same as the above-mentioned case of the gradation
correction, it is possible to avoid a case where the color position error
correction and the monochrome position error correction would be carried
out separately within a short span of time and downtime of the image
forming apparatus 1 would be increased.

[0133] It is noted that the above-mentioned determination as to whether
the correction execution is necessary is carried out by the writing
control part 121. Below, the determination as to whether the correction
execution is necessary according to the embodiment will be described with
reference to FIG. 17. FIG. 17 is a flowchart showing an operation of the
determination as to whether the correction execution is necessary carried
out by the writing control part 121 in a case where a job of forming and
outputting an image or images is input in the image forming apparatus 1
according to the embodiment.

[0134] As shown in FIG. 17, when the job is input to the image forming
apparatus 1 (step S1701) and a drawing command is input to the optical
writing apparatus control part 120 of the print engine 26 through the
engine control part 31, the writing control part 121 determines whether
an operation mode of the image forming apparatus 1 is a monochrome
preference mode (step S1702). The monochrome preference mode is an
achromatic color preference operation mode in which even if a full color
image is given, the given image is output as a monochrome image, as long
as no clear instruction for full color output is given. This operation
mode is set in the controller 20 of the image forming apparatus 1, and
the writing control part 121 determines the operation mode through the
engine control part 31.

[0135] In a case where the operation mode is the monochrome preference
mode (step S1702 YES), the writing control part 121 determines whether a
page to be output (i.e., printed) is of color or monochrome (step S1703).
This determination is not determination as to whether the original image
is of color or monochrome but determination as to whether a clear
instruction for color output is given although the operation mode is the
monochrome preference mode. That is, it is determined whether drawing
information input through a page memory is of color or monochrome.

[0136] In a case where the result of the determination of step S1703 is
monochrome output (step S1703 YES), the writing control part 121 carries
out determination as to whether the monochrome position error correction
is necessary (step S1704) and determination as to whether the monochrome
gradation correction is necessary (step S1705). In the determinations of
steps S1704 and S1705, the writing control part 121 reads the respective
ones of the count values "after monochrome position error correction
execution" and "after monochrome gradation correction execution",
compares them with the "position error correction execution necessary
threshold" and "gradation correction execution necessary threshold",
respectively, and determines whether the monochrome position error
correction and the monochrome gradation correction are necessary.

[0137] On the other hand, in a case where the result of the determination
of step S1702 is not the monochrome preference mode (step S1702 NO) or in
a case where the result of the determination of step S1703 is that the
next page to be output is not of monochrome (step S1703 NO), the writing
control part 121 carries out determination as to whether the full color
position error correction is necessary (step S1706) and determination as
to whether the full color gradation correction is necessary (step S1707).
The determinations of steps S1706 and S1707 are the determinations
described above with reference to FIGS. 15 and 16, and will be described
later in detail with reference to FIG. 18.

[0138] As described above, in the image forming apparatus 1 according to
the embodiment, it is determined whether the correction is necessary
based on the comparison of the output number of sheets count value that
is the information of the progress after the correction was carried out
last with the correction execution necessary threshold for each of color
and monochrome in principle. Further, it is determined that the
correction is unnecessary based on the comparison with the correction
execution unnecessary threshold.

[0139] However, in a case where it is determined that the correction is
necessary because the output number of sheets count value becomes equal
to or more than the correction execution necessary threshold for one of
color and monochrome, it is expected that, also for the other of color
and monochrome, the correction execution necessary threshold will be
reached shortly even though the output number of sheets count value has
not become equal to or more than the correction execution necessary
threshold yet but the output number of sheets count value has become
equal to or more than the correction execution unnecessary threshold. In
this case, in order to avoid a case where the color position error
correction and the monochrome position error correction would be carried
out separately within a short span of time, not only the correction for
the one of color and monochrome for which it has been determined that
execution is necessary, but the correction for full color is carried out,
according to the embodiment.

[0140] On this condition, the significance of the determinations of steps
S1702 and S1703 will now be described. The determinations of steps S1702
and S1703 are carried out in consideration that in the case of the
monochrome preference mode, it is considered that a frequency of
occurrences of forming and outputting full color images is low.
Therefore, in this case, even when the count value after the execution of
the correction for color has become equal to or more than the correction
execution unnecessary threshold as mentioned above, a period of time
taken for the count value after the execution of the correction for color
reaching the correction execution necessary threshold is not necessarily
short. Therefore, steps S1702 and S1703 are carried out.

[0141] That is, when the operation mode is the monochrome preference mode
in step S1702, the operation flow is switched to the side on which the
steps S1704 and S1705 are to be carried out. However, when the next page
is of color output, the count value of the number of sheets for color
will be increased although the operation mode is the monochrome mode, and
therefore, in this case, the operation flow is then returned to the side
on which the steps S1706 and S1707 are to be carried out. Thereby, it is
possible to avoid a case where even when the operation mode is the
monochrome preference mode, the frequency of the correction operations
for color would be increased meaninglessly because of applying the
embodiment.

[0142] When the operation of step S1705 or S1707 is completed, the writing
control part 121 carries out the correction operation according to the
corresponding determination result (step S1708), and subsequently,
carries out forming and outputting an image, i.e., drives the light
source apparatus(es) 281, forms electrostatic latent image(s) and carries
out development and transfer (step S1709). After the completion of
forming and outputting the image, the writing control part 121 determines
whether there is a next page to output (step S1710). Then, when there is
a next page (step S1710 YES), the process starting from step S1702 is
repeated. When there is no next page (steps S1710 NO), the process is
finished. Thus, in the image forming apparatus 1 according to the
embodiment, the operation carried out when the job to form and output an
image or images is input is completed.

[0143] Next, with reference to FIG. 18, details of the determinations as
to whether the full color correction is necessary, i.e., the processes of
steps S1706 and S1707 of FIG. 17, will be described. FIG. 18 is a
flowchart showing the details of determinations as to whether the
correction (i.e., adjustment) is necessary, carried out by the writing
control part 121. In FIG. 18, the determinations concerning the gradation
correction will be described as one example. The process of the
determinations concerning the position error correction are the same as
the process of the determinations concerning the gradation correction
merely except that the count values and the thresholds to read are
different, and duplicate description will be omitted.

[0144] As shown in FIG. 18, the writing control part 121 first determines
whether execution of the color gradation correction is necessary (step
S1801). That is, by comparing the count value of "after color gradation
correction execution" described above with reference to FIG. 14 with the
"gradation correction execution necessary threshold", the writing control
part 121 determines whether execution of the color gradation correction
is necessary.

[0145] In a case where the count value after the color gradation
correction execution is equal to or more than the gradation correction
execution necessary threshold (step S1801 YES), the writing control part
121 then determines whether execution of the monochrome gradation
correction is necessary (step S1802). That is, by comparing the count
value of "after monochrome gradation correction execution" with the
"gradation correction execution unnecessary threshold", the writing
control part 121 determines whether execution of the monochrome gradation
correction is necessary.

[0146] As described above with reference to FIGS. 15 and 16, in the case
where execution of the correction for color is necessary, execution of
the correction for monochrome is determined to be necessary when the
count value of "after monochrome gradation correction execution" becomes
equal to or more than, not the execution necessary threshold but the
execution unnecessary threshold. Therefore, in the determination of step
S1802, the writing control part 121 compares with the "gradation
correction execution unnecessary threshold".

[0147] In a case where it is determined in step S1802 that the count value
after the monochrome gradation correction execution is equal to or more
than the gradation correction execution unnecessary threshold (step S1802
YES), the writing control part 121 determines that the full color
gradation correction, i.e., the correction operation to be carried out by
drawing the patterns of FIG. 9, is necessary (step S1803).

[0148] On the other hand, in a case where it is determined in step S1802
that the count value after the monochrome gradation correction execution
is less than the gradation correction execution unnecessary threshold
(step S1802 NO), the writing control part 121 determines that the color
gradation correction, i.e., the correction operation to be carried out by
drawing the patterns of FIG. 13, is necessary (step S1804).

[0149] In a case where the count value after the color gradation
correction execution is less than the gradation correction execution
necessary threshold (step S1801 NO), the writing control part 121 then
determines whether execution of the color gradation correction is
undetermined (step S1805). In step S1805, by comparing the count value of
"after color gradation correction execution" with the "gradation
correction execution unnecessary threshold" described above with
reference to FIG. 14, the writing control part 121 determines whether
execution of the color gradation correction is undetermined.

[0150] In a case where the count value after the color gradation
correction execution is equal to or more than the gradation correction
execution unnecessary threshold (step S1805 YES), the writing control
part 121 then determines whether execution of the monochrome gradation
correction is necessary (step S1806). That is, in step S1806, by
comparing the count value of "after monochrome gradation correction
execution" with the "gradation correction execution necessary threshold",
the writing control part 121 determines whether execution of the
monochrome gradation correction is necessary.

[0151] It is noted that in a case where execution of the correction for
color is undetermined and execution of the correction for monochrome is
necessary, not only the correction for monochrome but the correction for
full color is carried out as described above with reference to FIGS. 15
and 16. Therefore, in the determination of step S1806, the writing
control part 121 compares with the "gradation correction execution
necessary threshold".

[0152] In a case where it is determined in step S1806 that the count value
after the monochrome gradation correction execution is equal to or more
than the gradation correction execution necessary threshold (step S1806
YES), the writing control part 121 determines that the full color
gradation correction, i.e., the correction operation to be carried out by
drawing the patterns of FIG. 9, is necessary (step S1803).

[0153] On the other hand, in a case where it is determined in step S1806
that the count value after the monochrome gradation correction execution
is less than the gradation correction execution necessary threshold (step
S1806 NO), the writing control part 121 determines that none of the
correction for monochrome and the correction for color is necessary, and
finishes the process.

[0154] In a case where it is determined in step S1805 that the count value
after the color gradation correction execution is less than the gradation
correction execution unnecessary threshold (step S1805 NO), i.e., in a
case where the color gradation correction is not necessary, the writing
control part 121 then determines whether execution of the monochrome
gradation correction is necessary (step S1807). In step S1807, by
comparing the count value of "after monochrome gradation correction
execution" with the "gradation correction execution necessary threshold"
described above with reference to FIG. 14, the writing control part 121
determines whether execution of the monochrome gradation correction is
necessary.

[0155] It is noted that in a case where the color gradation correction is
not necessary, the monochrome gradation correction becomes necessary only
in a case where the count value after the monochrome gradation correction
execution becomes equal to or more than the gradation correction
execution necessary threshold. Therefore, the process of step 1807 is the
same as the determinations of steps S1704 and S1705 of FIG. 17.

[0156] In a case where it is determined in step S1807 that the count value
after the monochrome gradation correction execution is equal to or more
than the gradation correction execution necessary threshold (step S1807
YES), the writing control part 121 determines that the monochrome
gradation correction is necessary (step S1808), and finishes the process.
On the other hand, in a case where it is determined in step S1807 that
the count value after the monochrome gradation correction execution is
less than the gradation correction execution necessary threshold (step
S1807 NO), the writing control part 121 determines that none of the
monochrome gradation correction and the color gradation correction is
necessary, and finishes the process. Thus, the determination as to
whether the correction is necessary according to the embodiment is
completed.

[0157] Thus, according to the embodiment, for each of color and
monochrome, based on the comparison between the output number of sheets
count value that is the information of the progress having occurred since
the correction was carried out last and the correction execution
necessary threshold, it is determined that the correction is necessary.
In a case where the output number of sheets count value becomes equal to
or more than the correction execution necessary threshold and thus it is
determined that the correction is necessary for one of color and
monochrome, not only the correction for the one of color and monochrome
thus determined necessary but the correction for full color is carried
out when the output number of sheets count value is equal to or more than
the correction execution unnecessary threshold for the other of color and
monochrome. This is because even when the output number of sheets count
value has not yet become equal to or more than the correction execution
necessary threshold for the other of color and monochrome, it is expected
that shortly the output number of sheets count value will reach the
correction execution necessary threshold also for the other of color and
monochrome. Thereby, in the optical writing apparatus included in the
image forming apparatus 1, it is possible to prevent that the correction
operations of color and monochrome would be separately carried out within
a short span of time, and to reduce consumption of developer and downtime
of the image forming apparatus 1 occurring because of the correction
(i.e., adjustment) operation of the optical writing apparatus.

[0158] It is noted that when the correction operation is carried out in
step S1708 of FIG. 17, the sensor control part 123 adjusts the amounts of
light of the light emission devices included in the pattern detection
sensor 117 as mentioned above. Also this adjustment operation is not
carried out each time when the correction operation is carried out, and
it is determined whether to carry out the adjustment operation based on
the conditions of the image forming apparatus 1. This determination will
now be described with reference to FIG. 19.

[0159]FIG. 19 is a flowchart showing the operation of determining whether
to carry out the adjustment of the amounts of light of the light emission
devices included in the pattern detection sensor 117. As shown in FIG.
19, when the correction operation is carried out, the sensor control part
123 first determines whether the job of forming and outputting an image
or images which is currently being processed is included in a series of
jobs, i.e., the same job as the job of forming and outputting an image or
images in which the adjustment of the amounts of light was carried out
previously (step S1901).

[0160] The significance of step S1901 is that when the job the same as the
job of forming and outputting an image or images in which the adjustment
of the amounts of light was previously carried out is being currently
processed, it can be expected that not so long period of time has elapsed
since the adjustment of the amounts of light was carried out previously.
Therefore, basically, it is determined that the adjustment of the amounts
of light is not necessary.

[0161] In a case where it is determined in step S1901 that the job
currently being processed is different from the job in which the
adjustment of the amounts of light was carried out previously (step S1901
YES), the sensor control part 123 determines whether the pattern
detection sensor 117 is emitting light (step S1902). It is noted that the
sensor control part 13 continues to emit light for a predetermined period
time after one printing job is finished, in order to avoid a useless
process that the pattern detection sensor 117 would be caused to stop
emitting light, then, within a short span of time, a printing job will be
input and thus, the pattern detection sensor 117 would be caused to start
emitting light again. The significance of step S1902 is that when the
pattern detection sensor 117 is emitting light, basically it is
determined that the adjustment of the amounts of light is not necessary.

[0162] When it is determined in step S1902 that the pattern detection
sensor 117 is emitting light (step S1902 YES), the adjustment of the
amounts of light is not necessary in principle as mentioned above.
However, the correction of the parameter values becomes necessary because
of a change in the conditions of the image forming apparatus 1 such as
the print engine 26 having been heated up, in a case where many pages
have been output (i.e., printed) within a short period of time, such as a
case where a job including many pages has been executed. Therefore, the
sensor control part 123 determines, as a progress having occurred from
the previous adjustment of the amounts of light, whether the number of
sheets having been output is equal to or more than 50 (step S1903).

[0163] When it is determined in step S1903 that the number of sheets
having been output since the previous adjustment of the amounts of light
is less than 50 (step S1903 YES), the sensor control part 123 determines
that the adjustment of the amounts of light is not necessary and finishes
the process. On the other hand, when it is determined in step S1903 that
the number of sheets having been output since the previous adjustment of
the amounts of light is equal to or more than 50 (step S1903 NO), the
sensor control part 123 carries out the adjustment of the amounts of
light (step S1905), waits for toner adhering to the conveyance belt 105
because of the adjustment of the amounts of light being cleaned (step
S1906), and finishes the process. It is noted that step S1906 is carried
out in a case where a toner mark or such formed on the conveyance belt
105 is used in the adjustment of the amounts of light of the light
emission devices as mentioned above.

[0164] In a case where it is determined in step S1902 that emitting of
light in the toner detection sensor 117 has been stopped (step S1902 NO),
the sensor control part 123 causes the toner detection sensor 117 to
start emitting light (step S1904), then carries out the adjustment of the
amounts of light (step S1905) and finishes the process after the cleaning
is finished (step S1906)

[0165] When it is determined in step S1901 that the job that is currently
being processed is the same as the job in which the adjustment of the
amounts of light was carried out previously (step S1901 NO), the
adjustment of the amounts of light is not necessary in principle as
mentioned above. However, the correction of the parameter values becomes
necessary because of a change in the conditions of the image forming
apparatus 1 such as the print engine 26 having been heated up, in a case
where the job that is currently being processed includes many pages and
thus, the many pages have been output (i.e., printed) within a short
period of time. Therefore, the sensor control part 123 determines, as a
progress having occurred from the previous adjustment of the amounts of
light, whether the number of sheets having been output is equal to or
more than 75 (step S1907).

[0166] When it is determined in step S1907 that the number of sheets
having been output since the previous adjustment of the amounts of light
is less than 75 (step S1907 NO), the sensor control part 123 determines
that the adjustment of the amounts of light is not necessary and finishes
the process. On the other hand, when it is determined in step S1907 that
the number of sheets having been output since the previous adjustment of
the amounts of light is equal to or more than 75 (step S1907 YES), the
sensor control part 123 carries out the adjustment of the amounts of
light (step S1905), waits for toner adhering to the conveyance belt 105
because of the adjustment of the amounts of light being cleaned (step
S1906) and finishes the process.

[0167] Thus, it is possible to avoid waste also concerning the number of
times of carrying out the adjustment of the amounts of light, and to
reduce downtime of the image forming apparatus 1. It is noted that the
number of sheets for the determination is different between steps S1903
and S1907. This is because in the case of the same job, i.e., in the case
of step 1907, outputting (i.e., printing) of respective pages is carried
out successively. In contrast thereto, in the case of the different job,
i.e., in the case of step S1903, it is expected that a time lag occurs
from the previous job being finished up to the current job being input.
As a result, in this case, it is expected that a relatively long time has
elapsed since the previous adjustment of the amounts of light. Therefore,
the threshold of the number of sheets (i.e., 50 sheets) for determining
that again adjusting the amounts of light is necessary is made smaller in
step S1903 than the threshold in step S1907 (i.e., 75 sheets).

[0168] It is noted that as shown in FIGS. 15 and 16, the thresholds for
determining whether the gradation correction is necessary are different
from the thresholds for determining whether the position error correction
is necessary. This is because it is necessary to carry out the
determination as to whether the position error correction is necessary
within a relatively short span of time because of distortion of the
reflection mirror 280 caused by heating, expansion or contradiction of
the conveyance belt 105 and so forth. Therefore, in the above-mentioned
embodiment, the thresholds are made different between the determination
as to whether the position error correction is necessary and the
determination as to whether the gradation correction is necessary. Other
than this configuration, for example, such a configuration may be
provided that in a case where it has been determined that the correction
is necessary in the determination as to whether the gradation correction
is necessary, also the position error correction is carried out
unconditionally in addition to the gradation correction.

[0169] In this case, instead of the stated order of the determination as
to whether the position error correction is necessary (steps S1704,
S1706) and the determination as to whether the gradation correction is
necessary (steps S1705, S1707) as shown in FIG. 17, the determination as
to whether the gradation correction is necessary is carried out first.
Thereby, it is possible to omit the determination as to whether the
position error correction is necessary in a case where it has been
determined that the correction operation is necessary in the
determination as to whether the gradation correction is necessary.

[0170] Further, in the above-mentioned embodiment, as shown in FIG. 17, it
is determined whether to carry out the correction operation, in a case
where a job of forming and outputting an image or images is input, as an
example. Alternatively, the determination as to whether the correction is
necessary may be carried out when power supply in the image forming
apparatus 1 is started, the image forming apparatus 1 is returned from a
power saving mode, or similar times. In this case, since input of a job
of forming and outputting an image or images is not a precondition, the
process of step S1703 of FIG. 17 is omitted, and thus, in a case of the
monochrome preference mode, the process proceeds directly to step S1704.

[0171] Further, in the above-mentioned embodiment, as described above with
reference to FIGS. 14 and 19, the count value of the number of sheets of
forming and outputting images is used as the information indicating the
progress having occurred since the correction operation was carried out
last or the progress having occurred since the adjustment of the amounts
of light was carried out last, and the thresholds are provided for the
count value of the number of sheets of forming and outputting images.
However, an embodiment of the present invention is not limited to this
configuration. The information indicating the progress is not limited to
the count value of the number of sheets of forming and outputting images,
and any other information may be applied to the information indicating
the progress, as long as the progress is determined which has occurred
since the correction operation was carried out last or the adjustment of
the amounts of light was carried out last. For example, information
indicating an elapsed period of time such as actual time, the number of
clock pulses of a clock that operates in the image forming apparatus 1,
or such, may be applied as the information indicating the progress.

[0172] The present invention is not limited to the specifically disclosed
embodiments, and variations and modifications may be made without
departing from the scope of the present invention.

[0173] The present application is based on Japanese priority application
No. 2010-061002 filed on Mar. 17, 2010, the entire contents of which are
hereby incorporated herein by reference.